1. Field of the Invention
The invention relates to novel microporous crystalline silicates and to processes for their preparation and use as adsorbents, drying agents, ion exchangers and catalysts or catalyst carriers for various catalytic processes.
More particularly, the present invention relates to a family of new microporous crystalline compositions, referred to herein as MSH-n compositions, having the general formula:Ar[Ms{(Si2O5)p(SiO2)q}].tH2O   (I)where (Si2O5)p(SiO2)q represents a silicate layer and M represents bridging groups interposed between adjacent silicate layers including one or more transition metals and A is an alkali or alkaline earth metal cation and water molecules occupy non-framework position in the composition as synthesized and where p and q are numbers having values representing a structure of the silicate layer, r is a number having a value representing the number of alkali and/or alkaline earth metal cations needed to render the composition neutral, s is a number having a value representing a number of bridging groups, and t is a number having a value representing the state of hydration of the composition. The present invention also describes processes for preparing the composition and methods for using the compositions.
2. Description of the Related Art
Zeolites are crystalline aluminosilicate molecular sieves that have microporous framework structures built from AlO4 and SiO4 tetrahedra. The tetrahedra are linked to form a structure that is characterized by the presence of micropores with dimensions in the range of 3 to about 15 Å and by the presence of exchangeable cations and sorbed molecules. Other classes of microporous oxide material that are not zeolites but which show similar ion exchange and molecule sorption properties such as aluminophosphates, U.S. Pat. No. 4,310,440, silicon substituted aluminophosphates, U.S. Pat. No. 4,440,871, and metal substituted aluminophosphates, U.S. Pat. No. 4,853,197 metallo zinc-phosphates, U.S. Pat. No. 5,302,362 have been described.
In addition to frameworks that are based on tetrahedral silicon or aluminum or metal oxide units, microporous compounds are also known that have frameworks constructed from octahedrally coordinated titanium, zirconium, or hafnium in combination with silicate or germanate tetrahedra For example U.S. Pat. Nos. 4,853,202, and 4,938,939, both issued to S. Kuzrnicki, describe the synthesis of microporous titanosilicates, whereas U.S. Pat. Nos. 5,891,417, and 5,888,472 both issued to Bem et al., describe microporous zirconium silicates and germanates. In addition to synthesized compositions, a large number of zirconium and titanium silicates are known to occur as minerals. Rocha and Anderson in the Eur. J. Inorg. Chem. 2000 801, provide a survey of the known mixed octahedral tetrahedral frameworks.
Notwithstanding the extensive previous work, a novel class of silicates containing vanadium and other metals with interstices of molecular dimensions, which are usually filled with water of hydration have been synthesized. The microporous silicates of the invention are characterized by their overall composition, their adsorption behavior and their ion exchange properties. The crystallinity of the various compounds follows from the fact that they all show a clear X-ray powder diffraction pattern.